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Earth history and life - 29202 > Trace fossils > Flashcards

Trace fossils Flashcards

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1
Q

What is another name for trace fossils?

A

Ichnofossils

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2
Q

What can trace fossils be used as?

A

Palaeoenvironmental indicators

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3
Q

What is endogenic trace fossils?

A

Made/ found within the rock (type of preservation)

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4
Q

What is epirelief trace fossil preservation?

A

Preserved on the top of beds

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5
Q

What is hyporelief?

A

Located at the base of beds

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6
Q

What is full relief?

A

Located within beds

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7
Q

What are exogenic traces?

A

Made on the sediment surface

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8
Q

How are full relief trace fossils preserved?

A

burrow preserved in 3d

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9
Q

What is another name for epirelief and hyporelief?

A

semi relief

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10
Q

Where is hyporelief most common?

A

Interbedded sands and muds

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11
Q

Where is an example of hyporelief?

A

Aberystwyth Grits (Silurian)

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12
Q

What are natural casts, true track, undertracks? (trace fossils)

A

Natural - made by infilling of original track
True - actual imprint
Undertrack - dent in sediment by animal pressure

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13
Q

What is the bias with trace fossils/ undertracks?

A

Bias towards heavier that can leave a greater impression

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14
Q

What is an example of undertrack preservation?

A

Sauropod footprints in the Morrison Formation Colorado

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15
Q

What problems are associated with trace fossil identification?

A

Single organism can produce many trace fossils
Different organism can produce similar trace fossils

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16
Q

What do invertebrate trace fossils names tend to reflect?

A

Morphology of trace (shape and ornamentation)

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17
Q

What can be used to describe the morphology of trace fossils?

A

Ichnogenus and Ichnospecies

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18
Q

How many trace fossils are produced by the Uca (modern day fiddler crab)?

A

4 traces

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19
Q

What are the trace fossils produced by Uca?

A

Psilonchnus - domichnion (living burrow)
Diplichnites - repichnion (walking trail)
Pascichnion - grazing trail
Coprolites - feacal pellets

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20
Q

What is the name for the resting trace? (cubchnia)

A

Rusophycus

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21
Q

What is the problem associated with identifying resting traces?

A

Originally thought just trilobites hunkering down on sediment but found other organisms can produce aswell

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22
Q

What are some examples of organisms which can produce resting fossils?

A

Polychaete worms
Snails
Brachiopod shrimps
Trilobites

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23
Q

What is repichnia?

A

walking or crawling trace

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24
Q

What is an example of a crawling trace?

A

Cruziana - Ordovician Anzaldo Fm Bolivia

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25
Q

What is an example of domichnion? (living burrow)

A

Arenicolites

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26
Q

What do arenicolites produce?

A

U shaped burrows which makes a worm cast and depression

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27
Q

What do arenicolite worm burrows do to the rock chemistry?

A

Anoxic rock is made oxygen rich by when oxygenated water is pulled into the sediment

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28
Q

What is the difference between diplocraterion and arenicorlite?

A

Scars of where burrow used to be (spreite)

29
Q

What is the name of the burrow behaviour of diplocraterion?

A

fugichnia - escape trace

30
Q

What is the ichnogenus and ichnospecies name of diplocraterion?

A

Diplocraterion yoyo

31
Q

Why is the name diplocraterion yoyo given?

A

Due to the changing position of the organism burrow due to erosion and deposition to avoid burial or exposure

32
Q

What is pascichnia? (trace fossil)

A

surface feeding trace

33
Q

What is an example of pascichnia?

A

Helminthoidea

34
Q

What is fodinichnia? (trace fossil)

A

Mining feeding trace

35
Q

What is an example of where fodinichnia can be found?

A

Chondrites in hardening sandstones from Ordovician Colorado
or
Zoophycos

36
Q

Where is fodinichnia produced in the sediment layers?

A

close to the water sediment interface

37
Q

Why is the pattern distribution in swooping motions for fodinichnia?

A

To avoid eating poop
Maximise exploited sediment

38
Q

What are chondrites produced by?

A

A worm

39
Q

What is agrichnia? (trace fossils)

A

Cultivation trace (hexagon pattern used to cultivate algae)

40
Q

What is an example of agrichnia trace?

A

Paleodictyon

41
Q

What trace fossil is the base of the cambrian defined by?

A

Phycodes

42
Q

What are hycodes followed by?

A

Trace fossil assemblage containing Rusophycos and Cruziana

43
Q

What are phycodes like?

A

Looping structure

44
Q

What is the prominence of Rusophycos and Cruziana appearing so early in the fossil record?

A

They precede trilobite body fossils

45
Q

What is tiering in trace fossils?

A

How many layers are exploited by burrowers

46
Q

What has happened to tiering over time?

A

Mid Ordovician 3 tiers
Remains like that till Early Jurassic
Then large diversification as deep seafloor exploited leading to 9 tiers in late cretaceous

47
Q

What are Thalassonoids?

A

Wide shape burrow produced by shrimp typical of littoral deposits (shore face)

48
Q

What are the names of trace fossil communities? (ichnofacies)

A

Nereites
Zoophycos
Cruziana
Skolithos
Scoyenia
Glossifungites

49
Q

What trace burrows make up the Nereite ichnofacie?

A

Spiroraphe
Lorenzinla
Chondrites
Paleodictyon
Nereites
Cosmorhaphe

50
Q

What are Nereite ichnofacies like?

A

Absence of vertical burrows
Deepwater environments
Found in muds (deposited from suspension)
Mud and siltstones of distal turbidites

51
Q

What traces make up Zoophycos ichnofacies?

A

Phycosiphon
Zoophycos
Spirophyton

52
Q

What are the characteristics of Zoophycos ichnofacies? (distribution, conditions)

A

Complex fodinichnia
Deep traces - Thalassinoides
Tiered arrangement
Abyssal to shallow continental shelf
Might occur in normal background conditions

53
Q

What traces are found in the Cruziana ichnofacie?

A

Asteriacites
Cruziana
Rhizocorallium
Aulichnites
Thalassinoides
Chondrites
Telchichus
Arenicolites
Rossella
Planolites

54
Q

What are the characteristics of Cruziana ichnofacies? (orientation, environment and position)

A

Horizontal and vertical burrows
Mid and distal continental shelf
Below normal wave base (storm activity potential)

55
Q

What traces make up the Skolithos ichnofacies?

A

Ophiomorpha
Diplocraterion
Skolithos
Monocraterion

56
Q

What are the characteristics of skolithos ichnofacies? (orientation, environment and sediment)

A

Low diversity vertical burrows
Intertidal situations
Sporadic sediment deposition (shifting sand and intertidal environments, storm sand sheets and top of turbidity flows)

57
Q

What are the trace fossil ichnofacies thought to be controlled by?

A

Sediment type
Water depth
Rate of deposition

58
Q

What is a sub trace fossil community?

A

Scoyenia ichnofacie
Glossifungite ichnofacie

59
Q

What traces make up the scoyenia ichnofacie?

A

Scoyenia
Acorichnus
Cruziana
Skolithos

60
Q

What traces make up the Glossifungite ichnofacie?

A

Thalassinoides
Bivalve boring
Polychaete burrows
Rhizocorallium
Psilonichus

61
Q

What are the characteristics of Glossifungite ichnofacies? (sediment, environment)

A

Sediment firm but not lithified (mud/ silt)
Low energy salt marshes, mud bars, high intertidal flats or shallow marine)

62
Q

What are the characteristics of scoyenia ichnofacies? (orientation, sediment)

A

Horizontal (occasionally vertical)
Fluvial and lacustrine sediment
Aeolian sands and paleosols

63
Q

What are some examples of substrate dependant trace fossils?

A

Teredolites (wood)
Trypanites (limestone)

64
Q

What traces make up the trypanites ichnofacies?

A

Echinoid grooves
Barnacle borings
Sponge borings
Polychaete worms
Bivalve boring
Sypuncullid boring

65
Q

What are the controls on distribution of trace fossil communities?

A

Average grain size of sediment
Sediment stability
Water content
Chemical conditions

66
Q

How does average grain size affect trace fossil community distribution?

A

Affect sediment ingesting burrowers
Organisms require particular sediment size to line burrow
Filter feeders avoid fine sediments

67
Q

How does water content affect trace fossil community distribution?

A

Affects consistency of sediment

68
Q

What are black shales have through to represent on the sea floor?

A

Soupy sediment cant burrow in

69
Q

How do chemical conditions affect trace fossil community distribution?

A

Oxygen levels are particularly important, with trace fossils being absent in totally
anoxic environments

Earth history and life - 29202 (29 decks)

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